Selective oxidation of alkyl aromatic compounds

ABSTRACT

ALKYL AROMATIC COMPOUNDS ARE TREATED WITH AN OXYGENCONTAINING GAS AT AN ELEVATED TEMPERATURE AND PRESSURE IN THE PRESENCE OF A LIQUID-WATER PHASE TO SELECTIVELY OXIDIZE SAID COMPOUND TO PREDETERMINED OXIDATION PRODUCTS AND PREFERABLY, ALCOHOLS AND ALDEHYDES OR KETONES.

United States Patent 3,714,263 1 SELECTIVE OXlDATION 0F ALKYL ARQMATIC CGMPOUNDS Henryk A. Cyba, Evanston, lill., assignor to Universal Oil Products Company, Des Plaines, Ill.

No Drawing. Continuation-impart of application Ser. No. 604,651, Dec. 27, 1966. This application Oct. 29, 1969, Ser. No. 872,401

' Int. Cl. C07c 49/76 U.S. Cl. 260-502 9 Claims ABSTRACT OF THE DISCLOSURE Alkyl aromatic compounds are treated with an oxygencontaining gas at an elevated temperature and pressure in the presence of a liquid-water phase to selectively oxidize said compound to predetermined oxidation products and preferably, alcohols and aldehydes or ketones.

BACKGROUND OF THE INVENTION Heretofore, the prior art has taught several process for the oxidation of alkyl aromatic compounds, and particularly, alkyl aromatic hydrocarbons to prepare oxidative products corresponding to the alkyl aromatic hydrocarbon, said oxidative products including acids, alcohols and aldehydes. For example, the prior art has taught that oxidation can be eifected in the gaseous phase and that, if the reaction is effected at temperatures above 300 C. such as about 335 C., the yield of certain oxidative products such as alcohols will be increased at the expense of the aldehydes and acids. Another prior art reference states that when the oxidative process is effected at temperatures ranging from about 225 to about 240 C., that only traces of the alcohol are produced even though the reaction is run in a water phase. This reference also teaches that the amount of water which is present in the reaction zone is at least three times as great by weight as that of the compound which is to undergo oxidation. Yet another reference which is found in the prior art teaches that oxidative products of organic compounds such as aldehydes, ketones, lactones and alcohols are produced by employing milder conditions of temperature and pressure along with the use of a catalyst comprising ionic bromine. These milder conditions include temperatures ranging from about 110 to about 150 C. and leads, at such low temperatures, to secondary oxidation products such as acids rather than primary oxidation products such as aldehydes, ke tones and alcohols. This reference also indicates that will be produced if the temperature and pressure were raised above these limits.

This application is a continuation-in-part of my co pending application, Ser. No. 604,651, filed Dec. 27, 1966, now abandoned.

The present invention relates to a process for the selective oxidation of alkyl aromatic compounds and particularly, to the selective oxidation of alkyl aromatic hydrocarbons. Specifically speaking, the invention is concerned with a process whereby an alkyl aromatic hydrocarbon may be selectively oxidized to form desired oxidation products which may be intermediates before the final oxidation product is prepared.

In contradistinction to the prior art, it has now been discovered that an alkyl aromatic hydrocarbon may be selectively oxidized in the presence of a liquid-water phase by treating said alkyl aromatic hydrocarbon with an oxygen-containing gas. The alkyl aromatic hydrocarbon is present in a large excess over the oxygen in the oxygen-containing gas, the ratio of alkyl aromatic hydrocarbon to oxygen being in the range of from about 20:1 to about 30:1 moles of alkyl aromatic hydrocarbon per mole of oxygen thereby contributing to insuring the fact that the oxidation product will comprise a favorable amount of alcohols and aldehydes or ketones. When the alkyl substituent is a methyl group the oxidation product comprise a favorable amount of benzyl alcohol and benzaldehyde; when the alkyl substituent is an ethyl group the oxidation product comprises a favorable amount of methylphenyl carbinol and acetophenone, and when the alkyl substituent is a propyl group the product comprises a favorable amount of ethylphenyl carbinol and ethylphenyl ketone.

It is therefore an object of this invention to provide a process for the selective oxidation of alkyl aromatic compounds.

A further object of this invention is to provide a process for the oxidation of alkyl aromatic hydrocarbons utilizing reaction conditions which will provide for the recovery of a favorable amount of intermediate oxidation products comprising alcohols and aldehydes and ketones.

In one aspect an embodiment of this invention resides in a process for the selected oxidation of an alkyl aromatic hydrocarbon to obtain an improved yield of the corresponding alcohol and aldehyde or ketone which comprises treating said hydrocarbon with an oxygen-containing gas at oxidation conditions in the presence of a liquid-water phase, the volumetric ratio of alkyl aromatic hydrocarbons to water being in the range of from about 5:1 to 20:1, and recovering the resultant oxidized products.

A specific embodiment of this invention is found in a process for the selective oxidation of toluene which comprises treating said toluene in a presence of a liquid- Water phase with oxygen at a temperature in the range of from about 200 to about 300 C. and a pressure in the range of from about 500 to about 200 pounds per square inch at a residence time in the range of from about 5 seconds to about 25 minutes and a mole ratio of 20 moles of toluene per mole of oxygen, and recovering the resultant benzyl alcohol and benzaldehyde.

Other objects and embodiments will be found in the following further detailed description of this invention.

As hereinbefore set forth, the present invention is concerned with a process for the seletive oxidation of alkyl aromatic hydrocarbons whereby products which are considered intermediates in the oxidation reaction may be obtained in greater yields than hereinbefore prepared. It has now been discovered that the obtention of these intermediate products can be attained by varying the reaction conditions, said reaction conditions including a predetermined residence time during which the alkyl aromatic hydrocarbon is in contact with the oxygen-containing gas as well as a relatively high mole ratio of alkyl aromatic hydrocarbon to oxygen. The reaction conditions under which the process of the present invention is effected will include temperatures in the range of from about 200 to about 300 C. or more and preferably within a range of from about 230 C. up to about 275 C. The reaction is effected at pressures ranging from about 500 up to about 2000 pounds per square inch or more, the amount of pressure which is utilized being that which is necessary to maintain a major portion of the reactants in the liquid phase. The reaction is further efiected in the presence of liquid water. However, as hereinbefore set forth, the amount of water which is present in the reaction is such that the volumetric ratio of alkyl aromatic hydrocarbon to water is in the range of tom about :1 to about 20:1 and preferably in a range of from about :1 to about :1. This is in contradistinction to the prior art which has taught that the amount of water which is present in the reaction zone is at least three times as great by weight as that of the alkyl aromatic hydrocarbon which is to undergo oxidation. That the amount of water present in the reaction zone is critical is born out by the fact that, when utilizing this large excess of water, only traces of tho alcohol product are obtained whereas, as will be hereinafter shown in greater detail, the combination of the liquidwater phase in which the alkyl aromatic hydrocarbon is present in a large excess over the Water with a corresponding high alkyl aromatic hydrocarbon-oxygen mole ratio, it will be possible to obtain high yields of the desired selective oxidation products comprising alcohols and aldehydes or ketones.

As hereinbefore set forth the combination of a liquidwater phase and a high ratio of alkyl aromatic hydrocarbon to oxygen results in the obtention of a high yield of selective oxidation products. The alkyl aromatic hydrocarbon which is to undergo selective oxidation is treated with an oxygen-containing gas at the preferred molar ratio of alkyl aromatic hydrocarbon to oxygen of 20:1 or more moles of alkyl aromatic hydrocarbon to oxygen, and preferably in a range of from about 20:1 to about :1 moles of alkyl aromatic hydrocarbon to oxygen, whereby the selective oxidation products comprising the alcohols and aldehydes or ketones are obtained. Examples of oxygen-containing gases which may be used include air, oxygen per se or oxygen admixed with an inert gas such as nitrogen, the only limitation being that the pressure formed by introducing the gas into the reactor be within the aforementioned ranges, and that the above ratio of alkyl aromatic hydrocarbon to oxygen is maintained. As hereinbefore set forth, the alkyl aromatic hydrocarbon should be in contact with the oxygen-containing gas for a predetermined residence time. The residence time which may be used will range from about 5 seconds up to about 25 minutes and will preferably be from a period of time ranging from 5 up to about 25 minutes. By increasing the charge rate of the hydrocarbon and by increasing the alkyl aromatic hydrocarbon to oxygen ratio, it has been found that a higher ratio of intermediate products such as the alcohols and aldehydes or ketones as compared o the final reaction product comprising the acid will be obtained.

It is contemplated within the scope of this invention that the process may, if so desired, be effected in the presence of a catalytic composition of matter. These catalytic compositions of matter will include the transition series metals of Groups I-B, IVB, V-B. VI-B, VII-B and VIII of the Periodic Table. These transition metals will include copper, silver, gold, titanium, zirconium, vanadium, tantalum, niobium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, platinum, palladium, ruthenium, rhodium, osmium, iridium, etc. The metals may be used per se or as oxides or salts thereof as well as combinations of the oxides or salts or as organomethalic complexes such as complexes 'of transition metals, typical examples of these metals being tungsten, molybdenum, iridium, etc. The forementioned oxides or salts may be deposited on a suitable carrier or soluble in water or in hydrocarbon solvents although, as hereinbefore set forth,

it is not considered a necessary limitation of the invention that the process utilize such catalysts.

The process of this invention may be effected in any suitable manner and may comprise either a batch or continuous type operation. For example, when a batch type operation is used, a quantity of the desired alkyl aromatic hydrocarbon is placed in an appropriate apparatus such as, for example, a rotating autoclave. In addition, a sufficient amount of water is added to the reactor so that a liquid phase between the alkyl aromatic hydrocarbon and the water is formed. The autoclave is sealed and heated to the desired temperature which, as hereinbefore set forth, may be in a range of from about 200 to about 300 C. and preferably in a range of from about 230 to about 275 C. The autoclave is heated to the desired temperature while an oxygen-containing gas is charged thereto. After the alkyl aromatic hydrocarbon has remained in contact with the oxygen-containing gas and water for a predetermined residence time, in a range hereinbefore set forth, the autoclave and contents thereof are allowed to cool to room temperature, the excess pressure is vented and the reaction product is recovered. This reaction prodnet is then subject to fractional distillation whereby the desired products comprising the aldehydes or ketones and alcohols are separated from the acid and unreacted alkyl aromatic hydrocarbon.

It is also contemplated within the scope of this invention that the process may be effected in a continual manner of operation. When such a type of operation is used, a reaction vessel is maintained at the proper operating conditions of temperature and pressure. The alkyl aromatic hydrocarbon which is to be oxidized is continuously charged to the reactor through one line, while water is charged thereto through a separate line. The aforementioned pressure under which the reaction vessel is maintained is provided for by the introduction of the oxygencontaining gas. Upon completion of the desired residence time, the reactor efiluent is continuously withdrawn and separated into the desired fractions, the water and unreacted alkyl aromatics being recycled to form a portion of the feed stock, while the oxidation products are withdrawn to storage.

Examples of selective oxidation products which may be prepared according to the process of this invention include benzyl alcohol, benzaldehyde, benzoic acid, methylphenyl carbinol, acetophenone, tolualdehyde, methylbenzyl alcohol, naphthyl alcohol, naphthaldehyde, naphtholic acid, etc. It is to be understood that the aforementioned oxidation products are only representative of the class of compounds which may be prepared and that the present invention is not necessarily limited thereto.

The following examples are given to illustrate the process of the present invention which however, are not intended to limit the generally broad scope of the present invention in strict accordance therewith.

EXAMPLE I The selective oxidation of toluene was effected in a continuous manner of operation by utilizing a stainless steel 300 ml. autoclave. Both toluene and air were introduced in the bottom of the autoclave which was maintained at a temperature ranging from 240 to 275 C. In addition, water was also introduced into the reactor at a low rate of 33 to 50 cc./hr. The charge rate of toluene to the autoclave was varied between 440 up to 845 cc./ hr., providing a volumetric ratio of toluene to water of about 11.8 to about 16.9. In addition, the molar ratio of toluene to oxygen was in a range of 2.05-2.27 to 0.1 mole of toluene per mole of oxygen. The residence time of toluene in the reaction zone was below 20 minutes. Upon completion of the desired residence time, the reactor efiluent was removed and subjected to analysis by means of a Gas-Liquid Chromatograph. The results are set forth in Table I.

TAB LE I Seleotivities, percent to- Hydrocarbon Benz- Molar ratio Penod Pressure Temp'eracharge, Water, Air, alde- Benzyl Benzoic of toluene o. (p.s.i.) ture, C. cc./l1r. cc./hr. s c.f./hr hyde alcohol acid to oxygen It is to be noted that by utilizing a relatively short residence time with a corresponding high feed rate of toluene and a high ratio of toluene to oxygen, it is possible to obtain lower ultimate yields of the completely oxidized product namely, benzoic acid and higher ultimate yields of what may be considered intermediate oxidation products, namely, benzyl alcohol and benzaldehyde.

EXAMPLE II In this example an autoclave similar in nature to that described in Example I above is maintained at a temperature range of from 230 C. to about 270 C. The feed stock comprising ethylbenzene along with air is introduced into the bottom of the reactor in such quantities that the molar ratio of ethylbenzene to air ranges from about 2:01. In addition, a small amount of water is also charged to the autoclave so that the volumetric ratio of ethylbenzene to water ranges from about 10:1 to about :1, said autoclave being continuously rotated during the residence time which ranges from about 5 to about minutes in duration. At the end of this time, the reactor efiiuent is continuously withdrawn and subjected to analysis by means of a Gas-Liquid Chromatograph. The

analysis will show that the major portion of the product will consist of methylphenyl carbinol and acetophenone in approximately equal amounts.

EXAMPLE III In this example a charge stock comprising methylnaphthalene is treated in a manner similar to that set forth in the above examples, that is, by charging said methylnaphthalene and air to an autoclave which is maintained at a temperature of about 275 C. under a pressure of about 1300 p.si., the molar ratio of methylnaphthalene to oxygen being about 2.5 :1. In addition, a sufficient amount of water is also charged to the autoclave to provide a volumetric ratio of methylnaphthalene to water of about 15: 1. After a predetermined residence time of 10 minutes has elapsed, the reactor efiiuent is removed and subjected to analysis by means of a Gas-Liquid Chromatograph. This analysis will disclose the presence of a major portion of naphthyl alcohol and naphthaldehyde in the product along with a minor amount of naphthoic acid.

Likewise, when propylbenzene is treated in an autoclave with air so that the mole ratio of propylbenzene to oxygen is 25:01 in the presence of a predetermined amount of water so that the volumetric ratio of propylbenzene to water is about 15:1 at a temperature of about 270 C. and an implied pressure of 1300 p.s.i. for a period of 10 minutes. The reactor effluent may be withdrawn and subjected to analysis. The Gas-Liquid Chromatographic analysis will disclose the presence of phenyl ethyl carbinol, phenyl ethyl ketone, benzyl methyl carbinol and benzyl methyl ketone, the first two main compounds being the predominant products.

EXAMPLE IV To illustrate the unexpected results which are obtained by utilizing the conditions of the instant process, namely, that the volumetric ratio of alkyl aromatic hydrocarbon to water should be in a range of from about 10:1 to about 20:1 and that the molar ratio of alkyl aromatic hydrocarbon to water should be in a range of from about 20:1 to :1 moles of alkyl aromatic hydrocarbon per mole of water a series of experiments were run utilizing the TABLE II Selec- Volume Percent Percent tivity ratio, converoxygen percent toluene: Temp sion of in off benzyl water C. toluene gas alcohol It is to be noted from the above Table that when the volume ratio of water to toluene was 1:1 there was only 0.5% conversion with no benzyl alcohol being formed, while when utilizing the conditions of the present process the oxidative selectivity of toluene to benzaldehyde and benzyl alcohol was over 34%. It is therefore readily apparent that by utilizing the conditions of the present application, it was unexpectedly found that a selective oxidation of an alkyl aromatic hydrocarbon to desired products, namely, alcohol and aldehydes could be obtained, said yields being totally unexpected in View of the prior art.

I claim as my invention:

1. A process for the selective oxidation of a hydrocarbon selected from the group consisting of mono-lower alkyl substituted benzenes and methylnaphthalene which comprises treating said hydrocarbon, at a temperature in the range of from about 200 C. to about 300 C., a pressure in the range of from about 500 to about 2000 p.s.i.g. and a residence time in the range of from about 5 seconds to about 25 minutes with an oxygen-containing gas in the presence of a liquid water phase, the volumetric ratio of hydrocarbon to water being in the range of from about 5:1 to 20:1, and recovering the resultant oxidized products.

2. The process as set forth in claim 1 in which said alkyl aromatic hydrocarbon is present in a mole ratio in the range of from about 20:1 to 30:1 moles of alkyl aromatic hydrocarbon per mole of oxygen.

3. The process as set forth in claim 1 in which said oxygen-containing gas is oxygen.

4. The process as set forth in claim 1 in which said oxygen-containing gas is air.

5. The process as set forth in claim 1 further characterized in that said process is elfected in the presence of a catalyst selected from the group consisting of transition metals, the oxides and salts thereof.

6. The process as set forth in claim 1 in which said alkyl aromatic hydrocarbon is toluene and said oxidized products comprise benzyl alcohol and benzaldehyde as major products.

7. The process as set forth in claim 1 in which said alkyl aromatic hydrocarbon is ethylbenzene and said oxidized products comprise methylphenyl carbinol and acetophenone as major products.

8. The process as set forth in claim 1 in which said alkyl aromatic hydrocarbon is methylnaphthalene and 3,047,616 7/ 1962 Blair et a1 260-599 said oxidized products comprise, naphthyl alcohol and 2,199,585 5/1940 Bone et a1 260592 naphthaldehyde as major products. 1,902,550 3/ 1933 Forrest et a1. 260-599 9. The process as set forth in claim 1 in which said 1,815,985 7/1931 Pansegrau 260-564 alkyl aromatic hydrocarbon is propylbenzene and said 5 2,565,087 8/1951 Porter et a1 260-631 oxidized products comprise ethylphenyl carbinol and ethyl V h l k t as major Products, HOWARD T. MARS, Primary Examiner References Cited P. H. LILES, Assistant Examiner UNITED STATES PATENTS 10 US. Cl. X.R.

3,073,867 1/1963 Offenhauer ct a1. 260592 260-500, 515 R, 524 -R, 599, 618 c 

